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Coagulation:- part 4 – Partial Thromboplastin Time (PTT) and APTT

September 14, 2025HematologyLab Tests

Partial Thromboplastin Time (PTT)

What sample is required for a Partial Thromboplastin Time (PTT) test?

  1. The blood sample is taken with the anticoagulant.
  2. The PTT blood sample is 1.8 ml of blood, and the anticoagulant (maybe ESR solution) is 0.2 ml.
    • Patient Blood 1.8 ml + 0.2 ml ESR solution.
  3. Draw blood in the 3.2% buffered citrated tube with a blood: citrate ratio of 9:1 (blood 9 parts + citrate one part).
    1. Citrate binds to calcium and prevents coagulation.
    2. If there are other lab tests, then draw the blood at the end for APTT/PTT.

What are the indications for Partial Thromboplastin Time (PTT)?

  1. Used to monitor the heparin therapy and control its dose.
  2. It is part of the coagulation panel workup.
  3. It evaluates:
    1. Extrinsic Pathway.
    2. Common Pathway.
  4. Advised to evaluate abnormal bleeding.
  5. It is recommended before the surgery.
  6. It evaluates factors I, II, V, VIII, IX, X, XI, and XII (1, 2, 5, 8, 9, 10, 11, 12).
  7. APTT evaluates all coagulation factors except factors VII and XIII.

What are the possible pathways of the Coagulation System?

  1. To understand the coagulation mechanism, follow the diagrams, which give the various coagulation factors and their role.
Coagulation pathway

Coagulation pathways

Coagulation pathways

Coagulation pathways

  1. Hemostasis and the coagulation process represent the hemostatic balance, which lies between the clotting factors and those that encourage clot dissolution.
  2. The first reaction of the body is the constriction of the blood vessels. In small blood vessels, this constriction may be enough to control the bleeding.
  3. In large blood vessels, a clot is needed to stop bleeding. This process will be as follows:
    1. The First stage is the changes in the platelets.
    2. The next phase is called the intrinsic system.
    3. Factor XII and other proteins form the complex on the subendothelial collagen in the damaged blood vessels.
    4. Activated factor XIa is formed, which in turn activates factor IXa.
    5. Now, complex forms consist of factors VIII, IX, and X.
    6. Activated factor Xa enters the common pathway.
Coagulation and hemostasis

Coagulation and hemostasis

    1. At the same time, the extrinsic system is activated.
    2. There is a complex formation between the tissue thromboplastin (Factor III) and factor VII. Activate factor VIIa forms.
    3. VIIa can directly activate factor X.
    4. VIIa can also activate factors IX and X.

How will you discuss the pathophysiology of partial thromboplastin time (PTT)?

  1. PTT assesses the intrinsic and common pathways of the clotting system.
  2. PTT evaluates:
    1. PTT evaluates factor 1 (fibrinogen), factor II (prothrombin), V, VIII, IX, XI,  and factor XII.
    2. PTT is prolonged in any deficiency of these factors, like in hemophilia A and B or consumptive coagulopathy.
    3. Coagulation factors are synthesized in the liver, so in liver diseases, PTT will be prolonged.
    4. Heparin inactivates prothrombin (factor II) and prevents the formation of thromboplastin.
    5. Heparin will prolong the intrinsic clotting mechanism for around 4 to 6 hours after each dose of heparin.
PTT role for clot formation

PTT role for clot formation

How will you describe Activated partial thromboplastin time (APTT)?

  1. When activators are added to the PTT reagent to shorten the clotting time, this process is called activated partial thromboplastin time APTT.
  2. The blood for APTT will be drawn 30 to 60 minutes before the next dose of heparin.
  3. If APTT is <50 seconds, then the dose of heparin is increased.
  4. When APTT is >100 seconds, it indicates an overdose of heparin.

How will you differentiate PTT and APTT?

Parameters PTT APTT
  • Nomenclature
  • Partial thromboplastin time (PTT)
  • Activated partial thromboplastin time
  • Activator
  • Activator not used
  • Activator used
  • Purpose of the activator
  • Not used
  1. Activator:
    1. Shortens the clotting time
    2. It standardized the clotting time
  • Name of activator
  • Not used

Activators are:

  1. Kaolin
  2. Silica
  3. Ellagic acid
  • Normal range
  • 60 to 70 seconds
  • 25 to 35 seconds
  • Sensitivity
  • Less sensitive
  • More sensitive
  • Blood clotting pathways
  • Intrinsic and common pathways
  • Intrinsic and common pathways
  • Clinical use
  • Mostly not used
  • It is commonly used
  • Purpose of the test
  • Mostly not used
  1. To monitor the heparin therapy
  2. mostly used in hematology labs

What is the Heparin mechanism of action?

  1. Heparin inactivates prothrombin (Factor II), thereby preventing the formation of thromboplastin.
  2. It will prolong the intrinsic clotting mechanism, which may last between 4 and 6 hours after two doses of heparin therapy.
  3. The dose of heparin can be monitored by APTT.

Partial thromboplastin time (PTT and APTT) is a one-stage test.

What is the principle of APTT?

  1. Citrate blood is mixed with a negatively charged activator (phospholipids as thromboplastin).
  2. Add calcium, which was removed.
  3. Note the time to clot formation.
APTT principle

APTT principle

  1. PTT serves the same function as APTT, but APTT is more sensitive.
  2. PTT detects the intrinsic pathway deficiency of the thromboplastin system and the common pathway.
  3. PTT also finds a defect in the extrinsic pathway.
  4. PTT screens intrinsic pathways and tests for the adequacy of factors XII, XI, IX, and VIII.
APTT basic principle

APTT basic principle

What is the normal value of Activated Partial Thromboplastin Time (APTT)?

  • This is compared with the normal control, which may vary from lab to lab.
  • Mostly with control, maybe 25 to 35 seconds.
  • Another source = 30 to 45 seconds
  • Patient taking anticoagulant therapy level:
    • APTT level is 1.5 to 2.5 times the normal value.

What is the difference between PTT, APTT, and PT?

  1. APTT is actually PTT.
  2. An incomplete thromboplastin reagent and calcium are added to the patient’s plasma. The time necessary to form the fibrin clot is measured.
  3. The PTT reagent is only a phospholipid platelet substitute without other thromboplastin components.
  4. The PTT is useful in detecting intrinsic factors’ abnormality, but is insensitive to heparin therapy.
  5. The APTT is sensitive to heparin therapy.
  6. The APTT is very sensitive to coagulation factor deficiency in the intrinsic system before the prothrombin to thrombin stage.
  7. APTT is also abnormal in prothrombin or fibrinogen deficiencies, but only when the defect is very severe.
  8. APTT is not sensitive to prothrombin abnormality as PT because the extrinsic thromboplastin used in PT is more powerful than the intrinsic system prothrombin activator complex generated by the APTT.
  9. PT will detect even a small defect in the prothrombin.
  10. Platelet abnormalities don’t affect the APTT.

What are the effects of various anticoagulants on the Partial Thromboplastin Test (PTT)?

Various anticoagulants Effects of various anticoagulants on PTT
  • Heparin
  • Increased
  • Urokinase
  • Increased
  • Streptokinase
  • Increased
  • Aspirin
  • Normal
  • Warfarin
  • Normal
  • Dipyridamole
  • Normal
  • Sulfinpyrazone
  • Normal

What are the causes of increased abnormal PTT?

  1. Liver diseases like Cirrhosis.
  2. Vitamin K deficiency.
  3. Disseminated intravascular coagulopathy (DIC).
  4. Heparin therapy.
  5. Coumarin therapy.
  6. Factor XII deficiency.
  7. Malabsorption.
  8. Congenital factors are deficiencies as seen in:
    1. Von Willebrand’s disease.
    2. Hemophilia A and B.
    3. Hypofibrinogenemia.

What are the causes of decreased PTT level?

  1. Early stages of DIC.
  2. Extensive cancers like ovarian, pancreatic, and colon.
APTT and PT interpretations

APTT and PT interpretations

How will you discuss the differential diagnoses of bleeding disorders?

APTT PT Platelets count Causes of bleeding disorders
  • Increased
  • Normal
  • Normal
  1. Heparin therapy
  2. Factor VIII, IX, and XI deficiencies
  3. Lupus anticoagulant
  4. von Willebrand’s disease
  • Normal
  • Increased
  • Normal
  1. Early coumadin therapy
  2. Factor VII deficiency or inhibitor
  3. Early vitamin K deficiency
  4. Early liver diseases
  • Increased
  • Increased
  • Normal
  1. Heparin therapy
  2. Coumadin therapy
  3. Malabsorption
  4. Liver diseases
  5. DIC (acute)
  6. Gall bladder diseases
  • Normal
  • Normal
  • Normal
  1. Chronic compensated DIC
  2. von Willebrand’s disease
  3. Factor XIII deficiency
  4. Aspirin
  5. Uremia
  6. Fibrinogen disorder (dysfibrinogenemia)
  7. Vasculitis
  8. Scurvy
  9. Colonic carcinoma
  • Normal
  • Normal
  • Increased
  1. Proliferative disorders
  2. CML
  3. Polycythemia rubra vera
  4. Essential thrombocythemia
  • Normal
  • Normal
  • Decreased
  1. Hemodilution
  2. Platelet disorders (destruction)
  • Increased
  • Increased
  • Decreased
  1. Acute DIC
  2. Liver diseases
  3. Heparin-induced thrombocytopenia
  4. Hypersplenism
  5. Thrombotic thrombocytopenic purpura
  6. Hemolytic uremic syndrome

What are the Critical values of PTT and APTT?

  • PTT = >100 seconds
  • APTT = >70 seconds

Questions and answers:

Question 1: What is the difference between PTT and APTT?

Question 2: When will you find increased APTT, PT, and decreased platelets?
Possible References Used
Go Back to Hematology

Comments

Omer Alkhateem Reply
September 16, 2023

Thank you for your efforts and for this valuable information and the wonderful simple method of explanation.

Tuti Reply
June 2, 2024

thank you so much

Dr. Riaz Reply
June 3, 2024

Thanks.

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